<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>时间小于 20:00 时，生成问候 "Good day"</title>
</head>

<body>
    <p>如果时间早于 20:00，会获得问候 "Good day"。</p>
    <button onclick="myFunction()">点击这里</button>
    <p id="demo"></p>
    <script>
        function myFunction() {
            var x = "";
            var time = new Date().getHours();
            if (time < 20) {
                x = "Good day";
            }
            document.getElementById("demo").innerHTML = x;
        }
    </script>
</body>

</html>